GS9090 Data Sheet
3.6.3 Switch Line Lock Handling
The principle of switch line lock handling is that the switching of synchronous video
sources will only disturb the horizontal timing and alignment of the stream, whereas
the vertical timing remains in synchronization.
To account for the horizontal disturbance caused by a synchronous switch, it is
necessary to re-synchronize the flywheel immediately after the switch has taken
place. Rapid re-synchronization of the GS9090 to the new video standard can be
achieved by controlling the flywheel using the FW_EN pin.
At every PCLK cycle the device samples the FW_EN pin. When the FW_EN pin is
set LOW anywhere within the active line, the flywheel will re-synchronize
immediately to the next TRS word.
The ability to manually re-synchronize the flywheel is also important when
switching asynchronous sources or to implement other non-standardized video
switching functions.
The GS9090 also implements automatic switch line lock handling. By utilizing both
the synchronous switch point defined in SMPTE RP168, and the automatic video
standards detect function, the device automatically re-synchronizes the flywheel at
the switch point. This will occur whether or not the device has detected TRS word
errors. Word alignment re-synchronization will also take place at this time.
Automatic switch line lock handling will occur regardless of the setting of the
FW_EN pin.
The switch line is as defined in Table 3-3.
Table 3-3: Switch Line Position for 270Mb/s Digital Systems
System
Video Format
Sampling
Signal
Standard
Parallel
Interface
Serial
Interface
Switch Line
Number
525
625
720x483/59.94 (2:1)
720x576/50 (2:1)
4:2:2
4:2:2
125M
125M
125M
259M-C
259M-C
10, 273
6, 319
BT.656
28201 - 1 July 2005
27 of 70
GENNUM [ GENNUM CORPORATION ]
